I am all for letters all the time, but there are some cases in which you should absolutely, every time send something tangible. No Facebook message, Tweet, or text is ever, ever, EVER a replacement for a sympathy letter. I know that they can be challenging to write; that you feel like you don't always know what to say, that you don't want to sound trite.
Fortunately, you are not alone. There are experts you can turn to in this for guidance. Most recently, I found a great wealth of points on what not to say in sympathy writing over at the European Paper Company blog. This article, written by Cole Imperi, really analysed some of the typical items mentioned in sympathy notes and had insights that I hadn't considered.
Most importantly to me, she said, "I didn’t say I knew or I understood when I really don’t know and I really don’t understand. Plus, I was positive. I wasn’t talking about death, I was talking about life. Be considerate of this when you sit down to write a sympathy note."
Thanks for the insights, Cole. I'd make you an honorary Alliance member, but the record shows you already are one. By the way, Cole frequently writes about episotolary issues on her own blog, Simplicity Embellished. It's worth checking out.